Lassa virus, endemic in West Africa, infects 100,000-300,000 people annually, killing 5,000-10,000, and leaving about 30,000 with residual sequelae such as nerve deafness. The overall goal of this grant proposal is to understand the protective immune response to Lassa virus, thus positioning us to develop a vaccine against Lassa fever. Lassa virus is a Biosafety level 4 (BSL4) agent, and the constraints imposed by this fact have significantly impeded our ability to study the agent. Nevertheless, vaccine studies were carried out almost a decade ago, in guinea pigs and primates, and showed clearly that protective immunity could be conferred against this disease. However, the protective component(s) of vaccine-induced immunity were not identified. We are now in a much stronger position to evaluate the protective components, and shall do so in the experiments we propose. Our group has extensive experience with emerging viruses in general, and Lassa virus in particular. In addition we have many years of experience in designing vaccines against Old World arenaviruses. The constructs we will use will exploit recent advances that greatly enhance the immune responses induced by DNA vaccines, optimizing the induction of T cells (CD8+ and CD4+), and antibodies. There are only two reliable challenge models for Lassa fever, guinea pigs and primates. The Scripps collaborators will first evaluate the immunogenicity of the vaccines in guinea pigs with immunized animals also being sent to USAMRIID for live virus challenge trials. In the second year the study will then move to the primate models in Houston, where we will use rhesus macaques (Indian origin) characterized in the MAMU I allele in order to evaluate the immune response in primates in a model that closely parallels the human responses to the same viral antigens. Finally the vaccinated monkeys will be moved to USAMRIID where challenge studies will be performed under the supervision of Dr. Peter B. Jahrling, and where all the collaborators will combine efforts on site to ensure an exhaustive evaluation of the responses of the individual primates. These studies are expected to lead to the identification of a candidate Lassa vaccine that can be tested in humans.